Semiconductor device and its manufacturing method

ABSTRACT

A semiconductor device having, on a silicon substrate, a gate insulating film and a gate electrode in this order; wherein the gate insulating film comprises a nitrogen containing high-dielectric-constant insulating film which has a structure in which nitrogen is introduced into metal oxide or metal silicate; and the nitrogen concentration in the nitrogen containing high-dielectric-constant insulating film has a distribution in the direction of the film thickness; and a position at which the nitrogen concentration in the nitrogen containing high-dielectric-constant insulating film reaches the maximum in the direction of the film thickness is present in a region at a distance from the silicon substrate. A method of manufacturing a semiconductor device including introducing nitrogen by irradiating the high-dielectric-constant insulating film which is made of metal oxide or metal silicate, with a nitrogen containing plasma, is also provided.

This is a Continuation of U.S. application Ser. No. 10/519,084 filedDec. 23, 2004, which is based on 371 National Stage Application No.PCT/JP03/07761 filed on Jun. 19, 2003, which claims priority fromJapanese Patent Application No. 2002-187596 filed on Jun. 27, 2002, thedisclosure of which are incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device having ahigh-dielectric-constant thin film and a manufacturing method thereof,and more particularly to an art making a gate insulating film thatconstitutes a MOSFET (Metal Oxide Semiconductor Field Effect Transistor)attain higher performance and lower power consumption.

2. Description of the Related Art

As a material for the gate insulating film of the MOSFET, the siliconoxide film is in wide use having an excellent process stability and ahigh insulation capability. Meanwhile, along with the currentminiaturization, the thickness of the gate insulating film has beendecreasing, and in the device whose gate length is 100 nm or less, ithas become essential under scaling low that the film thickness of thesilicon oxide film which serves as a gate insulating film is 1.5 nm orless. Yet, when such an extra thin insulating film is utilized, thetunneling current through the insulating layer, in applying the gatebias, becomes substantial in comparison with the source/drain current,which leads to a serious adverse effects on attempts to attain higherperformance and lower power consumption for the MOSFET.

Another problem to accompany the reduction of the thickness of the gateinsulating film is the diffusion of the dopants from the gate electrode(the polysilicon electrode). The gate electrode used in the MOSFET, ingeneral, acquires its metallic properties through the high concentrationdoping which is applied to the polysilicon grown on the gate insulatingfilm, and, thus, when the silicon oxide film is very thin, there arisesa problem that the dopants may diffuse from the gate electrode to thesilicon substrate side, passing through the insulating film layer.

In order to solve the above problems of the increase in leakage currentand the penetration of the dopants that are brought about by thereduction of the film thickness of the gate insulating film, varioustechniques have been being developed. One of such techniques is a methodin which by adding nitrogen to the silicon oxide film, the dielectricconstant of the film is made higher than that of the pure silicon oxidefilm and thereby the effective (electrical) film thickness of the gateinsulating film is made lessened without reducing its physical filmthickness. Since it was, furthermore, confirmed that the nitrogenaddition also suppresses the diffusion of dopants within the insulatingfilm, and, therefore, the technique of the nitrogen addition to the gateinsulating film has been drawing considerable attention as a highlypromising technique capable to solve the two problems mentioned above.However, this technique has, as pointed out, disadvantages that thenitrogen addition to the silicon oxide film can only raise itsdielectric constant up to a certain value and besides nitrogen may causethe interfacial defects and the fixed charge generation in the film,resulting in the poor mobility as well as the lower reliability of thetransistor.

In consequence, the investigations are under way to find a materialhaving a dielectric constant higher than those of the silicon oxynitridefilm and the silicon nitride film as well as an preventive effect on thedopant diffusion to replace the silicon oxide film as the nextgeneration material of the gate insulating film. Firstly, amongmaterials having a high dielectric constant, Al₂O₃, ZrO₂, HfO₂,rare-earth element oxides such as Y₂O₃, and lanthanoid type rare-earthelement oxides such as La₂O₃ and, in addition, thin films of silicate ofthese substances are being examined as candidates for such a material.

This is based on an idea that even if the gate length becomes minute,the use of a high-dielectric-constant film of this sort makes itpossible to prevent the tunneling current well with a film thickness thescaling law allows to have, while maintaining the capacitance of thegate insulating film at the same time.

Now, for any type of the gate insulating film, the film thickness of theinsulating layer obtained by the reverse calculation from the gatecapacitance under the assumption that the material of the gateinsulating film is a silicon oxide film is called the film thickness interms of the silicon oxide film thickness. That is, when the dielectricconstants of the insulating film and the silicon oxide film are taken tobe ∈_(h) and ∈_(o), respectively, and the thickness of the insulatingfilm is taken to be dh, the film thickness in terms of the silicon oxidefilm thickness de becomes de=dh (∈_(o)/∈_(h)). This implies, in otherwords, that, with the material having a dielectric constant ∈_(h) thatis larger than ∈_(o) the insulating film with a certain thickness maybecome equivalent to a thin silicon oxide film. As the dielectricconstant ∈_(o) of the silicon oxide film is 3.9 or so, if ahigh-dielectric-constant film, for example, with ∈_(h)=39 is used, thefilm 15 nm thick has a film thickness of 1.5 nm in terms of the siliconoxide film thickness so that this film can heavily reduce the tunnelingcurrent.

As described above, in developing the next generation MOSFET, varioushigh-dielectric-constant films are, as the gate insulating filmmaterial, being examined for use, and the afore-mentioned metal oxidethin films and silicate thin films are regarded as strong candidates forthe high-dielectric-constant film. Nevertheless, even thesehigh-dielectric-constant films have been shown to have the followingproblems.

Firstly, the thermal stability of the high-dielectric-constant film isitself a problem. Namely, it has been reported that, in the step ofconducting the heat treatment to activate dopants implanted in the gateelectrode, the afore-mentioned gate material with a high dielectricconstant becomes crystallized or the interfacial reaction with thesilicon substrate proceeds. When crystallization of thehigh-dielectric-constant film takes place, with the boundary (grainboundary) appearing among grains, the insulation characteristics onthese grain boundaries deteriorate and the film thickness within a planebecomes non-uniform due to crystallization is brought about. As themeans of overcoming this problem of crystallization, it is effective toselect a high-dielectric-constant material with a high thermalstability, in the first place, and besides apply the nitrogen additionto the metal oxide or silicate film. Meanwhile, oxygen in the vaporphase readily diffuses into the high-dielectric-constant film so that areactive layer may be disadvantageously formed on the interface with thesilicon substrate at the time of the film growth and the subsequent heattreatment.

In regard to this problem, a structure in which a very thin (normally0.5 nm to 1 nm or so thick) silicon oxide film is inserted on theinterface between a high-dielectric-constant film and a siliconsubstrate is being examined. Moreover, a recent report indicated that asilicon oxynitride film can be used as the afore-mentioned interfacialinsertion layer with effect.

As the second problem for the high-dielectric-constant gate insulatingfilm, similar to the silicon oxide film, deterioration of the devicecharacteristics thereof due to the dopant penetration is well known.While seriousness of this problem varies with the material type of theinsulating film, and, moreover, the physical film thickness for thehigh-dielectric-constant gate insulating film can be set thicker thanthat for the silicon oxide film, if the diffusion rate of the dopants inthe film is high and a polysilicon gate electrode or polysilicongermanium electrode is utilized, this problem becomes a fatal one.Nevertheless, the recent investigation demonstrated that nitrogenaddition to Al₂O₃ or ZrO₂ can suppress the dopant diffusion well.

For the third problem, there is pointed out deterioration of electriccharacteristics of the interface between a high-dielectric-constant thinfilm and a silicon substrate. Compared with the interface of theconventional silicon oxide film, the interface of thehigh-dielectric-constant thin film has a higher interfacial defectdensity of, in general, not less than 10¹¹/cm², which is liable to causethe following problems. These interfacial defects (or defects within thefilm) worsen the MOSFET mobility in such a way that it may become evenless than a quarter of that with the silicon oxide film. Further, thepresence of fixed charges in the film and on its interfacedisadvantageously varies the threshold of the transistor operations. Fora remedy of these problems, like the remedy of the first problem, theinsertion of a silicon oxide film is effective. However, if theinterfacial silicon oxide film layer is thick, the film thickness of thewhole gate insulating film in terms of the silicon oxide film thicknessincreases a great deal. On the other hand, if the interfacial oxide filmlayer is thin, satisfactory interfacial thermal stability or sufficientpreventive effects on the dopant penetration cannot be obtained.Furthermore, although the structure in which an extra thin siliconoxynitride film or silicon nitride film is inserted on the interfacebetween a high-dielectric-constant film and a silicon substrate iseffective for the improvement on the interfacial thermal stability andsuppression of the dopant penetration, deterioration of electriccharacteristics remains. This can be attributed to the interfacialdefects caused by the additional presence of nitrogen and, in comparisonwith the conventional interface of the silicon/silicon oxide films, moredeterioration of the mobility and reliability is brought about.

As described above, although the first and the second problems can besuccessfully overcome by making nitrogen contained in thehigh-dielectric-constant gate insulating film, once inside, the presenceof the nitrogen on the interface with the silicon substrate has adverseeffects. In making nitrogen contained in the silicon oxide film, if thesample is subjected to a heat treatment in the atmosphere of a nitrogencontaining gas such as NH₃ or NO gas, nitrogen can be introduced intothe film, but a large amount of segregated nitrogen tends to be left onthe interface with the silicon substrate, which causes the lowering ofthe mobility and the deterioration of the reliability as described forthe third problem. Further, for the high-dielectric-constant insulatingfilm, too, nitrogen can be introduced into the film by annealing that inthe atmosphere of a nitrogen containing gas, but, in this case, too, apossibility of a similar problem of nitrogen segregation on theinterface with the silicon substrate cannot be ruled out.

As another method of introducing nitrogen into ahigh-dielectric-constant thin film, there is proposed to use the step ofapplying an oxidation treatment to a metal nitride film (Koyama et al.,Tech. Dig. IEDM. 2001, p. 459). In short, a ZrN film is grown on thesurface of a silicon substrate by the sputtering method, and by applyingan oxidation treatment thereto at 500° C., nitrogen is added into ZrO₂and thereby a better thermal stability than the conventional ZrO₂ filmcan be provided. However, in this method, when ZrN is grown as well aswhen the oxidation treatment is conducted, a SiON layer containingnitrogen at a high concentration is formed on the interface with thesilicon substrate so that this method either cannot bring a thoroughsolution for the third problem described above.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor devicehaving a gate insulating film structure capable to operatesimultaneously measures which are, in applying thehigh-dielectric-constant gate insulating film to the device, devised toimprove the afore-mentioned thermal stability, suppression of the dopantpenetration and interfacial electric characteristics and a manufacturingmethod thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing one embodiment of a semiconductordevice according to the present invention, and FIG. 2 is a flow diagramshowing one embodiment of a manufacturing method of a semiconductordevice according to the present invention.

FIG. 3 is a schematic view showing another embodiment of a semiconductordevice according to the present invention. Further, FIG. 4 is a graphshowing the results of the measurements of the nitrogen profile in theAl₂O₃ film (the results of the secondary ion mass spectroscopy) withnitrogen being introduced into the film by the nitrogen plasmairradiation.

FIG. 5 is a graph showing the bonding state analysis for the surface ofthe hafnium silicate subjected to the plasma nitridation treatment,obtained by the X-ray photoelectron spectroscopy.

FIG. 6 is a flow diagram showing another embodiment of a manufacturingmethod of a semiconductor device (a manufacturing method of a gateinsulating film structure which comprises an oxidation treatment appliedto a layered structure having a metal nitride layer) according to thepresent invention, and FIG. 7 is a flow diagram showing anotherembodiment of a manufacturing method of a semiconductor device (amanufacturing method of a gate insulating film structure which comprisesan oxidation treatment applied to a layered structure having a siliconnitride film) according to the present invention.

Referential numerals used in the drawings are described below.

Referential numeral 101 indicates a silicon substrate; referentialnumeral 102, a silicon oxide film (an interfacial oxide film layer);referential numeral 103, a nitrogen containing high-dielectric-constantinsulating film; referential numeral 104, agate electrode; referentialnumeral 201, a silicon substrate; referential numeral 202, a hydrogenterminal surface; referential numeral 203, a silicon oxide film;referential numeral 204, a metal layer; referential numeral 205, anitrogen containing layer; referential numeral 206, a nitrogencontaining high-dielectric-constant insulating film; referential numeral301, a silicon substrate; referential numeral 302, a silicon oxide film;referential numeral 303, a nitrogen containing high-dielectric-constantinsulating film; referential numeral 304, a gate electrode; referentialnumeral 601, a silicon substrate; referential numeral 602, a hydrogenterminal surface; referential numeral 603, a silicon oxide film;referential numeral 604, a metal Zr deposition layer; referentialnumeral 605, a Zr deposition layer; referential numeral 606, a nitrogencontaining high-dielectric-constant insulating film; referential numeral701, a silicon substrate; referential numeral 702, a hydrogen terminalsurface; referential numeral 703, a silicon oxide film; referentialnumeral 704, a HfSi deposition layer; referential numeral 705, a siliconnitride film; referential numeral 706, a nitrogen containinghigh-dielectric-constant insulating film (a nitrogen containing Hfsilicate layer).

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The present invention provides, as a first embodiment, a semiconductordevice stacked a gate insulating film and a gate electrode in this orderon a silicon substrate; wherein

said gate insulating film comprises a nitrogen containinghigh-dielectric-constant insulating film which has a structure in whichnitrogen is introduced into metal oxide or metal silicate; and

the nitrogen concentration in said nitrogen containinghigh-dielectric-constant insulating film has a distribution in thedirection of the film thickness; and

a position at which the nitrogen concentration in said nitrogencontaining high-dielectric-constant insulating film reaches a maximum inthe direction of the film thickness is present in a region at a distancefrom the silicon substrate.

It is favorable that in this semiconductor device, a position at whichthe nitrogen concentration in said nitrogen containinghigh-dielectric-constant insulating film reaches a maximum in thedirection of the film thickness is present in a region at a distance ofnot less than 0.5 nm from the silicon substrate.

Further, it is also favorable that a position at which the nitrogenconcentration in said nitrogen containing high-dielectric-constantinsulating film reaches a maximum in the direction of the film thicknessis localized on the side of a gate electrode in said nitrogen containinghigh-dielectric-constant insulating film.

It is also favorable that a position at which the nitrogen concentrationin said nitrogen containing high-dielectric-constant insulating filmreaches a maximum in the direction of the film thickness is localized inthe central section of said nitrogen containing high-dielectric-constantinsulating film.

The nitrogen concentration on a silicon substrate side interface of saidgate insulating film is favorably less than 3 atomic %.

The present invention provides, as a second embodiment, a semiconductordevice stacked a gate insulating film and a gate electrode in this orderon a silicon substrate; wherein

said gate insulating film comprises a nitrogen containinghigh-dielectric-constant insulating film which has a structure in whichnitrogen is introduced into metal silicate; and

a nitrogen atom in said nitrogen containing high-dielectric-constantinsulating film selectively bonds with a silicon atom in metal silicate.

It is favorable that, in this semiconductor device, a nitrogen atomwhich selectively bonds with a silicon atom in said metal silicate issituated at a distance from the silicon substrate.

It is favorable, in this semiconductor, said gate insulating filmcomprises a silicon oxide film formed on said silicon substrate so as tobe in contact therewith, and said nitrogen containinghigh-dielectric-constant insulating film formed on said silicon oxidefilm so as to be in contact therewith.

The present invention provides, as a third embodiment, a semiconductordevice stacked a gate insulating film and a gate electrode in this orderon a silicon substrate; wherein

said gate insulating film comprises a nitrogen containinghigh-dielectric-constant insulating film which has a structure in whichnitrogen is introduced into metal silicate; and

the composition of said nitrogen containing high-dielectric-constantinsulating film continuously varies in the direction of the filmthickness and the silicon concentration has a minimum value in themiddle section lying between a silicon substrate side interface of saidnitrogen containing high-dielectric-constant insulating film and a gateelectrode side interface thereof; and

nitrogen is introduced only into a region lying between the position atwhich the silicon concentration has the minimum value and said gateelectrode side interface.

The present invention provides, as a fourth embodiment, a semiconductordevice stacked a gate insulating film and a gate electrode in this orderon a silicon substrate; wherein

said gate insulating film has a layered structure having, from thesilicon substrate side, a first silicon oxide film, a metal oxide filmor a metal silicate film and a second silicon oxide film; and

only the second silicon oxide film has a structure in which nitrogen isintroduced into silicon oxide.

It is favorable that, in the above semiconductor device, said siliconsubstrate and said gate insulating film are in contact with each other,and said gate insulating film and a gate electrode are in contact witheach other; and

said gate electrode is made of either a polysilicon or a polysilicongermanium conductive film.

It is favorable that, in the above semiconductor device, said gateinsulating film contains at least one type selected from the groupconsisting of Zr, Hf, Ta, Al, Ti, Nb, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb and Lu.

Further, the present invention provides a method of manufacturing asemiconductor device stacked a gate insulating film and a gate electrodein this order on a silicon substrate; wherein

said semiconductor device is a semiconductor device of theafore-mentioned first, second and third embodiment: which comprises thestep of

making said introduction of nitrogen by irradiating said high-dielectricconstant insulating film which is made of metal oxide or metal silicate,with a nitrogen containing plasma.

The present invention provides a method of manufacturing a semiconductordevice stacked a gate insulating film and a gate electrode in this orderon a silicon substrate; wherein

said semiconductor device is a semiconductor device of theafore-mentioned fourth embodiment: which comprises the step of

making said introduction of nitrogen by irradiating said layeredstructure with a nitrogen containing plasma.

The present invention provides a method of manufacturing a semiconductordevice stacked a gate insulating film and a gate electrode in this orderon a silicon substrate; wherein

said semiconductor device is a semiconductor device of theafore-mentioned second embodiment; which comprises the step of

irradiating said high-dielectric constant insulating film which is madeof metal silicate, with a nitrogen containing plasma, so as to form,selectively, bonds between silicon and nitrogen in metal silicate, andthereby making said introduction of nitrogen.

The present invention provides a method of manufacturing a semiconductordevice stacked a gate insulating film and a gate electrode in this orderon a silicon substrate; wherein

said semiconductor device is a semiconductor device of theafore-mentioned first, second or third embodiment, which comprises thestep of

forming, on the silicon substrate, a layered structure made of a metallayer and a nitrogen containing layer that contains nitrogen, andthereafter applying an oxidation treatment to form a gate insulatingfilm.

It is favorable that, in this manufacturing method, said nitrogencontaining layer is one of a silicon oxynitride film and a siliconnitride film.

Further, it is also favorable that, in this manufacturing method, saidnitrogen containing layer is a metal nitride film.

Further, it is also favorable that, in this manufacturing method, saidlayered structure is formed after a silicon oxide film with a filmthickness of less than 1 nm is formed on the surface of the siliconsubstrate.

Further, the present invention provides a semiconductor device stacked agate insulating film and a gate electrode in this order on a siliconsubstrate; wherein

said gate insulating film contains nitrogen and metal oxide or metalsilicate; and

the nitrogen concentration in said gate insulating film has adistribution in the direction of the film thickness; and

a position at which the nitrogen concentration in said gate insulatingfilm reaches a maximum in the direction of the film thickness is presentin a region at a distance from the silicon substrate.

The present invention sets forth a gate insulating film structurewherein a position at which the nitrogen concentration in thehigh-dielectric-constant insulating film reaches the maximum ispreferably set at a distance of not less than 0.5 nm from the siliconsubstrate interface, and the nitrogen concentration on the interfacebetween the high-dielectric-constant gate insulating film and thesilicon substrate is preferably set as low as less than 3%. Further, ina manufacturing method to attain the present gate insulating filmstructure, the control on the nitrogen distribution in the gateinsulating film may be achieved by comprising the step of nitridingselectively a region other than the vicinity of the silicon substratethrough the exposure to a nitrogen containing plasma or the step offorming, on the silicon substrate, a layered structure composed of ametal layer and a nitrogen containing layer, and thereafter applying anoxidation treatment thereto.

The high dielectric constant as used herein means the dielectricconstant higher than that of the silicon nitride film. In practice, fromthe viewpoint of making the film thickness in terms of the silicon oxidefilm thickness thin, the dielectric constant of thehigh-dielectric-constant gate insulating film is set to be preferablynot less than 8 and more preferably not less than 10. However, whenalumina is utilized as metal oxide, it is sufficient to set not lessthan 7.

A semiconductor device having a typical high-dielectric-constant gateinsulating film structure in accordance with the present invention isshown in FIG. 1. Herein, the description is made, taking, as an example,a gate insulating film structure composed of a nitrogen containinghigh-dielectric-constant insulating film 103 and a silicon oxide film102, which is formed by making nitrogen localized in the upper layersection of a high-dielectric-constant thin film made of either metaloxide or metal silicate so as to form the nitrogen containinghigh-dielectric-constant insulating film 103 and then inserting an extrathin interfacial oxide film layer (a silicon oxide film 102) betweenthis thin film and the silicon substrate 101.

First, the effects of the gate insulating film structure shown in FIG. 1are described below. The addition of nitrogen to metal oxide or metalsilicate can improve thermal stability of the high-dielectric-constantthin film. Further, thermal stability of the interface between thehigh-dielectric-constant thin film and the silicon substrate can beimproved by laying the extra thin silicon oxide film 102 on theinterface between the high-dielectric-constant thin film and thesubstrate. Meanwhile, because the nitrogen presence at a highconcentration is localized in the upper section of thehigh-dielectric-constant thin film, the dopant penetration from the gateelectrode can be well suppressed. As regards electric characteristics ofthe interface with the silicon substrate, since thehigh-dielectric-constant film does not come into direct contact with thesilicon substrate but the extra thin silicon oxide film is laidtherebetween, and nitrogen in the film is absent on the interface of thesilicon substrate so that interfacial defect density can be reduced andthe deterioration of the mobility and the reliability, suppressed.

Further, there are various other methods considered possible to use as amanufacturing method of a gate insulating film of the present invention,and the method wherein the high-dielectric-constant film is selectivelynitrided by irradiation with a nitrogen containing plasma as describedbelow, and the method in which nitrogen is introduced and its profile iscontrolled by the step of oxidizing a layered structure of a metal layerand a nitrogen containing layer are, for example, proved to besatisfactory.

In the first method making use of plasma irradiation, a gate insulatingfilm (without nitrogen introduction) comprising ahigh-dielectric-constant insulating film is formed on a siliconsubstrate and the irradiation with active nitrogen formed by plasma isapplied thereto. For instance, it is possible to form ahigh-dielectric-constant film made of metal oxide or metal silicate andirradiate the surface of this high-dielectric-constant insulating filmwith a nitrogen containing plasma. Through proper adjustments of theconditions for the plasma generation, active nitrogen which is highlyreactive with elements constituting the gate insulating film or thehigh-dielectric-constant insulating film can be supplied. This enablesthe reaction between nitrogen and the above element to proceed speedily,and suppressing the nitrogen diffusion into the gate insulating film,prevents nitrogen from reacting the silicon substrate so that only thefilm surface (or the region other than the interface with the siliconsurface) can be selectively nitrided. In other words, the nitrogenprofile can be localized in a region (the surface side) at a distancefrom the silicon substrate interface.

Further, in the second manufacturing method, the nitrogen concentrationprofile in the film can be controlled by the oxidation treatment of thelayered structure shown in the flow diagram of FIG. 2. For instance,after an extra thin silicon oxide film 203 is formed on the surface(hydrogen terminal surface 202) of a silicon substrate 201 (FIG. 2( b)),a metal layer 204 that is a layer made of metal is grown on the surfaceof this oxide film (FIG. 2( c)). Following that, after a metal nitridelayer is grown as a nitrogen containing layer 205 that is a layercontaining nitrogen on the top of the metal layer and a layeredstructure is fabricated (FIG. 2( d)), a heat treatment is appliedthereto in the oxygen atmosphere, which enables the metal layer to beoxidized and at the same the nitrogen concentration in thehigh-dielectric-constant insulating film to be localized in the vicinityof the surface layer. In this way, a nitrogen containinghigh-dielectric-constant insulating film 206 having such a nitrogenconcentration profile as shown in FIG. 2( e) can be obtained, whereby agate insulating film composed of the nitrogen containinghigh-dielectric-constant insulating film 206 and the silicon oxide film203 can be formed. For the nitrogen-containing layer, herein, the use ofnitride film or a silicon nitride film (a oxynitride film) of a metalelement capable to constitute metal oxide is effective. Further, as amethod well-suited to grow metal nitride, the reactive sputtering methodwith a metal nitride target or a metal target can be given.

The thickness of the nitrogen containing layer is preferable to be notless than 1 nm from the viewpoint of suppressing the dopant diffusion,but not greater than 2 nm on the ground that an unduly large amount ofnitrogen does not provide such a large effect as increased in proportionto the amount of added nitrogen.

The conditions of the oxidation treatment may be appropriatelydetermined depending on the material, but the temperature can be set at500 to 900° C., for instance.

After the gate insulating film is formed on the silicon substrate asdescribed above, agate electrode is formed thereon by a known method andthereby a semiconductor device of the present invention may be obtained.

In the structure of a semiconductor device of the present invention, theaddition of nitrogen into the gate insulating film comprising ahigh-dielectric-constant film improves the thermal stability, suppressesthe penetration of dopants from the gate electrode side and, at the sametime, overcomes the problems of poor mobility and deterioration of thereliability by keeping nitrogen in the gate insulating film away fromthe silicon substrate interface and restricting the presence of nitrogento the film surface or the central section therein.

The nitrogen distribution in the gate insulating film which provides theabove effects is not limited to the profile shown in the schematic viewof FIG. 1, and various profiles shown in FIG. 3 are also found to beeffective. FIG. 3( a) illustrates a case that nitrogen is distributedalmost uniformly in one section of the high-dielectric-constantinsulating film 303, wherein nitrogen concentration rapidly drops on theinterface between the high-dielectric-constant film and the siliconoxide film 302 which is laid on the interface between thehigh-dielectric-constant insulating film and the silicon substrate 301,and nitrogen is absent in the silicon oxide film 302 which is insertedon the interface. FIG. 3( b) shows a case that the maximum of thenitrogen concentration is situated in the central section of thehigh-dielectric-constant insulating film (the presence of nitrogen isrestricted to its central section) and, in this case, too, the nitrogenconcentration rapidly drops towards the interface between thehigh-dielectric-constant film and the silicon oxide film and nitrogen isabsent on the interface with the silicon substrate. Further, FIG. 3( c)with a profile shape indicating that nitrogen presence is localized tothe surface side (the gate electrode side) if thehigh-dielectric-constant insulating film presents a case that somenitrogen has segregated on the interface between thehigh-dielectric-constant film and the silicon oxide film, owing to thenitrogen diffusion in the high-dielectric-constant insulating film orsuch. If the distance between the interface between the silicon oxidefilm and the silicon substrate and the region to which nitrogen presenceis localized is less than 1 nm, such a case is certainly disadvantageousbecause, under certain circumstances, fixed charges on the interface,resulting from the nitrogen presence, may lead to the deterioration ofthe mobility and the reliability. However, when the region wherenitrogen is localized (the maximum value of the nitrogen concentrationin the direction of the film thickness within nitrogen containinghigh-dielectric-constant insulating film) is at a distance of preferablynot less than 0.5 nm and more preferably not less than 1 nm from thesilicon substrate, and besides the nitrogen concentration in thevicinity of the silicon surface interface is sufficiently low, thestructure shown in FIG. 3( c), not to mention FIG. (1), FIG. 3( a) and(b), can provide an excellent semiconductor device. Although thepermissible nitrogen concentration on the silicon substrate interfaceobviously depends on the acceptable degree of the mobility deteriorationand the reliability deterioration for a particular element (the devicedesign), it is, in this instance, preferable that the nitrogenconcentration on the silicon substrate interface of the gate insulatingfilm is less than 3 atomic % from the viewpoint of the interfacialelectric characteristics and more preferable that none of nitrogen ispresent on the substrate interface, at all. Further, the maximumnitrogen concentration in the gate insulating film is preferable toattain not less than 1 atomic % to attain thermal stability and thesuppressing effect of the dopant penetration. On the other hand, themaximum nitrogen concentration in the film is preferably less than 20atomic %, viewed from the point of insulation characteristics and thereliability of the gate insulating film. Nevertheless, the range ofnitrogen concentration is closely related to the design of elementcharacteristics and not limited to the above range.

When a silicon oxide film is first formed on the surface of the siliconsubstrate and thereafter a layered structure made of a metal layer and anitrogen containing layer is formed thereon and an oxidation treatmentis applied thereto to form a gate insulating film, the film thickness ofthis silicon oxide film is set to be preferably less than 1 nm with theview of reducing the film thickness of the gate insulating film in termsof the silicon oxide film thickness for a given physical film thicknessthereof, but preferably not less than 0.5 nm from the viewpoint ofinterfacial electric characteristics.

With respect to the film thickness of the nitrogen containinghigh-dielectric-constant gate insulating film, although varying withcircumstances, for example, it is considered that, from the viewpoint ofpreventing a rapid increase in existing leakage current level, thephysical film thickness of the gate insulating film is preferably set tobe not less than 1.5 nm, and the present invention can well apply tosuch a gate insulating film. When the position of the maximum nitrogenconcentration in the direction of the film thickness is set at adistance of not less than 0.5 nm from the silicon substrate, the gateinsulating film requires, as a necessity, a film thickness exceeding 0.5nm.

Further, examples of the material for the high-dielectric-constantinsulating film where nitrogen is to be introduced include ZrO₂, HfO₂,Ta₂O₅, Al₂O₃. TiO₂, Nb₂O₅, rare-earth element oxides such as Sc₂O₃ andY₂O₃, oxides of lanthanoid type elements such as La₂O₃, CeO₂, Pr₂O₃,Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃,Lu₂O₃ and, in addition, silicate materials which are formed by addingsilicon to these above metal oxides.

Further, apart from the structures as shown in afore-mentioned FIG. 1 toFIG. 3 wherein an extra thin silicon oxide film is laid on the interfacebetween a high-dielectric-constant insulating film and a siliconsubstrate, with the view of improving interfacial electriccharacteristics, there can be given, effectively, another structurecomprising an extra thin silicon oxide film laid on the top of ahigh-dielectric-constant insulating film in order to improve electriccharacteristics of the interface with a gate electrode (for example, apolysilicon electrode or a polysilicon germanium electrode) that is tobe set on the top of a gate insulating film, wherein a silicon oxidefilm layer on the surface side (on the gate electrode side) (or in aregion at a distance from the silicon substrate interface) can beselectively nitrided. In this case, the gate insulating film has, forinstance, a layered structure having, from the silicon substrate side, afirst silicon oxide film, a film made of either metal oxide or metalsilicate and a second silicon oxide film, and nitrogen is introducedonly into the second silicon oxide film, while no nitrogen is introducedinto the first silicon oxide film or the film made of either metal oxideor metal silicate.

The film thickness of the above first and second silicon oxide films areboth preferably set to be not less than 0.5 nm from the viewpoint ofimproving interfacial electric characteristics, but not greater than 1nm with the view of reducing the film thickness of the gate insulatingfilm in terms of the silicon oxide film thickness for a given physicalfilm thickness thereof. Further, the film thickness of theafore-mentioned film made of either metal oxide or metal silicate ispreferably set to be not less than 2 nm from the viewpoint ofsuppressing the tunneling current but not greater than 5 nm, for thesake of convenience in production and proportion in the form of thesemiconductor device.

Further, apart from the afore-mentioned layered structures made of asilicon oxide film/a high-dielectric-constant insulating film/a siliconoxide film with clear interfaces, a structure wherein the composition ina metal silicate thin film moderates in the direction of the filmthickness and the silicon component is raised in an upper layer sectionand a lower layer section of the gate insulating film as described inJapanese Patent Application Laid-open No. 358225/2001, and only theregion on the surface side where the silicon concentration is high isselectively nitrided demonstrates its effect. In this gate insulatingfilm structure, the gate insulating film comprises a nitrogen containinghigh-dielectric-constant insulating film which has a structure in whichnitrogen is introduced into metal silicate, the composition in thenitrogen containing high-dielectric-constant insulating filmcontinuously varies in the direction of the film thickness, and thesilicon concentration has the minimum value in the middle section lyingbetween a silicon substrate side interface of the nitrogen containinghigh-dielectric-constant insulating film and the other gate electrodeside interface thereof, and nitrogen is introduced only into a regionlying between the position at which the silicon concentration has theminimum value and the gate electrode side interface, and none ofnitrogen is introduced into a region lying between the position wherethe silicon concentration has the minimum value and the siliconsubstrate side interface. In such a structure, because the concentrationof the metal element in metal silicate increases in the middle section,and the silicon component increases in an upper layer section and alower layer section of the film, on the both of boundaries of the gateinsulating film with the silicon substrate (the lower side interface)and with the gate electrode (the upper side interface), structuressimilar to the SiO₂/Si interface can be each formed, and interfacialelectric characteristics can be improved. Further, although the silicatematerial with a high metal concentration is known to have a disadvantageof having a relatively low crystallizing temperature, its thermalstability can be heightened by forming a structure in which this metalhigh concentration region is placed between two silicon highconcentration regions which have high thermal stability.

When the nitrogen containing high-dielectric-constant insulating film inwhich the composition of metal silicate varies in the direction of thefilm thickness is considered to be divided into three layer-shapedregions, that is, from the side of the silicon substrate, a firstregion, a middle region and a second region, (a first region is incontact with the silicon substrate and the second region, the gateelectrode), there can be given, as an example of the above structure, anembodiment wherein the silicon concentration in metal silicate decreasescontinuously from the silicon substrate side interface in the firstregion, and takes the minimum value and immediately afterwards starts toincrease in the middle region, and then continues to increase up to theinterface on the gate electrode side in the second region, while thesilicon/metal element ratio in the first and second regions are higherthan the average value for the whole gate insulating film and thesilicon/metal element ratio in the middle region is lower than theaverage value for the whole gate insulating film, and nitrogen isintroduced into the second region only. In such a case, the thickness ofthe first and the second regions are both preferably set to be not lessthan 0.5 nm from the viewpoint of improving interfacial electriccharacteristics, but not greater than 1 nm with the view of reducing thefilm thickness of the gate insulating film in terms of the silicon oxidefilm thickness for a given physical film thickness thereof. Further, thethickness of the middle region is preferably set to be not less than 2nm from the viewpoint of suppressing the tunneling current but notgreater than 5 nm, for the sake of convenience in production andproportion in the form of the semiconductor.

Further, in introducing nitrogen into the high-dielectric-constantinsulating film or the silicon oxide film, there can be consideredseveral types of bonding styles (metal-nitrogen bond, silicon-nitrogenbond and oxygen-nitrogen bond) with any of the metal elementconstituting the metal oxide or the metal silicate layer and silicon insilicate as well as silicon and oxygen constituting the silicon oxidefilms inserted on the upper layer or the lower layer of thehigh-dielectric-constant film. A substance held by bonds between a metalatom and a nitrogen atom, out of these bonds, provide, in most cases,relatively poor insulation so that, in introducing nitrogen into thefilm, it is preferable to form a structure wherein silicon atoms areselectively nitrided, by preventing the metal-nitrogen bonds to beformed too many. However, as far as Al is concerned, because aluminiumnitride (AlN) is a material capable to provide a good insulation, anyconsideration is unnecessary in this respect when the nitridationtreatment for the Al₂O₃ material is made. In a structure wherein siliconatoms are selectively nitrided, there certainly exist moresilicon-nitrogen bonds than metal-nitrogen bonds.

In the case that agate insulating film (without nitrogen introduction)comprising a high-dielectric-constant insulating film is formed on asilicon substrate and an irradiation with a nitrogen containing plasmais applied thereto, for example, when either a layered structure havinga silicon oxide film and a high-dielectric-constant thin film made ofmetal oxide or a metal silicate thin film is subjected to a plasmanitridation treatment, it is possible to nitride only silicon atoms inthe film (especially on the film surface side) through appropriateadjustments of the conditions for the plasma irradiation.

EXAMPLES

Examples of a semiconductor device having a high-dielectric-constantgate insulating film structure in accordance with the present inventionand a manufacturing method thereof are described below.

Example 1

In the First Example of the present invention, the results of nitrogenintroduction made by an irradiation of nitrogen radicals into anAl₂O₃film grown by the Atomic Layer Chemical Vapor Deposition (ALD)method are described.

On a silicon wafer, a field region of MOSFET was formed beforehand and,in this region, a silicon oxide film with a thickness of 0.6 nm wasformed as an underlying oxide film (an interface oxide film). After anAl₂O₃ film with a thickness of 4 nm was grown on this wafer by the ALDmethod in which Al(CH₃)₃ and H₂O source gasses were supplied thereforalternatively, irradiation with nitrogen radicals was applied to thissurface. The radical irradiation was made by a vacuum apparatus carryingan ECR (Electron Cyclotron Resonance) radical source as a plasma source.The radical source was disposed directly 20 cm above from the wafer andthe conditions for the nitrogen radical irradiation was set such thatthe substrate temperature was 300 to 700° C., the pressure, 0.3 to 0.9Pa and the electric power, 150 W, and thereunder the nitridationtreatment was carried out for 30 minutes.

FIG. 4 shows the analyzed results of secondary ion mass spectroscopicmeasurements for the nitrogen concentrations in the Al₂O₃ films forwhich nitridation was carried out under typical but various conditionsfor the radical irradiation. These results demonstrate that when thefilm was nitrided under the condition that the substrate temperature washigh and the nitrogen gas pressure was low (700° C., 0.3 Pa), nitrogenwas distributed throughout the whole film and even introduced to theinterface at a high concentration, while in the case that the conditionemployed was that the substrate temperature was low and the nitrogen gaspressure was high (300° C., 0.9 Pa), the nitrogen concentration in thefilm decreased but the nitrogen profile obtained showed localization onthe surface side. Therefore, it is possible to regulate the amount ofthe nitrogen introduced into the film through the substrate temperatureand besides localize the nitride concentration in the film on the filmsurface side by setting the nitrogen gas partial pressure optimal (inthe above case, a higher pressure).

Using these films subjected to the nitridation treatment as thehigh-dielectric-constant gate insulating films and polysilicon doped athigh concentration as gate electrodes, MOSFETs were fabricated, and itwas confirmed that all the samples show an improvement on thermalstability and clear effect of suppressing dopant penetration. Further,the mobility evaluation for these transistors established that themobility for the transistor (condition for nitridation: 300° C., 0.9 Pa)having a gate insulating film structure in which nitrogen is localizedon the surface side of the Al₂O₃ film increased by approximately 20% incomparison with that of the transistor (condition for nitridation: 700°C., 0.3 Pa) with a gate insulating film having a high nitrogenconcentration on its interfaces.

Example 2

In the Second Example, the nitridation treatment was made by irradiatinghafnium silicate (HfSiO) with a nitrogen plasma.

On a silicon wafer, a field region of MOSFET was formed beforehand and,in this region, a silicon oxide film with a thickness of 0.6 nm wasformed as an underlying oxide film (an interface oxide film). A silicatefilm with a thickness of 3 nm containing 10 atomic % of Hf was formedthereon, and, using an RCR plasma source, active nitrogen formed fromnitrogen gas was applied thereto. The condition for irradiation was thatthe substrate temperature was 300° C., the nitrogen partial pressure,6.7 Pa and the additional power supply, 60 W for 1 minute. Resultingfrom this, a silicate film containing 10 atomic % of nitrogen wasobtained.

The secondary ion mass spectroscopic measurements were made as in FirstExample, and it was observed that nitrogen distribution in the film hada peak at a position 0.5 nm away from the film surface side and that thenitrogen content gradually decreased with increasing depth and nitrogenwas absent on the interface with the silicon substrate. X-rayphotoelectron spectra (Si 2p core level spectra) of a Hf silicate filmof the present example, before and after the plasma irradiation areshown in FIG. 5. In this result, the peak at 102.5 eV associated withsilicate is shifted towards the lower binding energy side by thenitridation treatment. This indicates the formation of the Si—N bond inthe film. Meanwhile, the Hf 4f spectrum shows no change and appears atthe normal position of hafnium silicate after the nitridation, whichconfirms that no Hf—N bond was formed in the film. These resultsdemonstrate that silicon atoms of hafnium silicate on the surface sidewere selectively nitrided by the nitridation treatment described above.When a MOSFET with this hafnium silicate film as agate insulating filmwas fabricated, as the formation of the Hf—N bonds were suppressed inthe step of selective nitridation, any increase in leakage current wasnot detected, compared with a transistor with untreated hafnium silicate(that is, without nitrogen introduction). Further, an improvement onthermal stability by the effects of nitrogen introduction was observed(crystallization temperature was improved by 100° C. or more), while thedeterioration of the mobility or the reliability, which oftenaccompanies the nitrogen introduction was not.

Moreover, the effect of suppressing the dopant penetration frompolysilicon gate was established. In the present example, the Si—O bondsin the silicate film were selectively substituted to the Si—N bonds and,as a result, nitrogen was successfully contained in the silicate filmwithout increasing the leakage current and, at the same time, thenitrogen introduction had an effect of increasing the dielectricconstant (the average dielectric constant of the silicate film increasedfrom 10 to 12). Further, when zirconium silicate and lanthanum silicate,instead of hafnium silicate, were in the same fashion nitrided, similareffects were obtained.

Example 3

In the Third Example of the present invention, referring to a flowdiagram of FIG. 6, there is described an example in which nitrogenaddition was made to a ZrO₂ high-dielectric-constant thin film with anextra thin silicon oxide film being laid on the silicon substrateinterface thereof.

After cleaning a silicon wafer 601, a chemical oxide film formed on thesubstrate surface was peeled off by a treatment with a hydrofluoric acidsolution to make the silicon surface terminate with hydrogen atoms (FIG.6( a)). This wafer was then subjected to an oxidation treatment in thelow pressure oxygen atmosphere at 5 Torr (670 Pa) and 700° C. to form asilicon oxide film 603 with a thickness of 0.6 nm (FIG. 6( b)). A metallayer and a nitrogen-containing layer were then grown on the surface ofthis oxide film, using a sputtering system equipped with a plurality oftargets. For the sputtering deposition, the low damage deposition methodmaking use of the ECR (Electron Cyclotron Resonance) discharge wasemployed, and argon gas was used as the sputtering gas, and the gaspressure and high frequency output were set to be 5×10⁻⁴ Torr (0.067 Pa)and 100 W, respectively. After a metal Zr layer 04 was grown to athickness of 2 nm on the aforementioned silicon oxide film 603 with thesubstrate temperature set at the ambient temperature, (FIG. 6( c)), aZrN layer 605 was grown to a thickness of 1.0 nm with targets exchangedand the substrate temperature set at the ambient temperature, whereby alayered structure of ZN/Z/SiO₂ was formed (FIG. 6( d)). The oxidationtreatment of this sample was conducted in the low pressure oxygenatmosphere at 1 Torr (130 Pa) and 500° C. The metal layer (the metalnitride layer) was converted into a ZrO₂ (ZrON) layer by the oxidationtreatment, whereby a high-dielectric-constant insulating film (ZrONhigh-dielectric-constant film) 606 containing nitrogen was obtained.Analysis of the composition distribution in the direction of the filmthickness by the secondary ion mass spectroscopy revealed that nitrogenwas localized around a position 0.6 nm away from the film surface andthe maximum nitrogen concentration was 10 atomic %. Further, it wasconfirmed that the SiO₂ composition was maintained on the interface withthe silicon substrate.

After that, by forming a polysilicon electrode on a gate insulating filmhaving the silicon oxide film 603 and the high-dielectric-constantinsulating film 606 fabricated by the above method, a MOSFET wasfabricated. With the gate insulating film capacitance as well as thecurrent-voltage characteristics being measured for this MOSFET device,its film thickness in terms of the silicon oxide film thickness was 1.4nm, and the value of the leakage current through the gate insulatingfilm was found to be lowered by approximately three orders of magnitude,compared with the silicon oxide film with the corresponding filmthickness. Further, the crystallization temperature of the gateinsulating film layer was improved by 150° C. or more, compared withthat without nitrogen addition. Further, a heat treatment carried out at1050° C. in the step of activating the dopants did not lead to theabnormality in the characteristics of the transistor operation whichtends to arise accompanying the dopant penetration.

Example 4

In the Fourth Example, after a ZrO₂ film in which nitrogen was localizedon the surface side was fabricated by the same method as in the ThirdExample, a polysilicon germanium electrode was formed as a gateelectrode. In comparison with the Third Example (a polysilicon gateelectrode), a decrease in depletion of the gate electrode and anincrease in ON-current of the transistor were attained thereby.

Example 5

In the Fifth Example, nitrogen addition was made through a siliconnitride film into a Hf silicate high-dielectric-constant thin filmwherein a silicon oxide film was laid on a silicon substrate interface(FIG. 7).

As in the Third Example, after cleaning a silicon wafer 701 and peelingoff a chemical oxidation film (FIG. 7( a)), a silicon oxide film 703with a thickness of 0.6 m, was formed (FIG. 7( b)). On the surfacethereof, an amorphous HfSi layer 704 with a physical thickness of 2 nmwas formed by means of the sputtering deposition with a sintered HfSitarget (FIG. 7( c)). The condition for the sputtering deposition was thesame as in the Second Example. After that, on the surface of this wafer,a silicon nitride film 705 with a thickness of 0.5 nm was grown by meansof the CVD (Chemical Vapor Deposition) using SiH₄ and NH₃ as sourcegasses (FIG. 7( d)). The sample was subjected to the oxidation treatmentin the low pressure oxygen atmosphere at 1 Torr (130 Pa) and 700° C. toform a nitrogen-introduced hafnium silicate (HfSiO) film 706, whereby anitrogen containing high-dielectric-constant gate insulating film wasformed.

Analysis of the composition distribution of the present sample by thesecondary ion mass spectroscopy revealed that although some mixing tookplace at the atomic layer level due to the interfacial reactions on oneinterface between the silicon oxide film and the Hf silicate as well ason the other interface on the surface side, that is, between the Hfsilicate layer and the silicon nitride film (the silicon oxynitridefilm), the nitrogen concentration peak has the maximum value of 10atomic % at a position 0.5 nm away from the surface, and furtherconfirmed that the SiO₂ composition was maintained on the interface withthe silicon substrate.

Now, a MOSFET device was fabricated by forming a gate electrode on agate insulating film comprising a silicon oxide film 703 and a hafniumsilicate layer 706, which was formed as described above. In this MOSFET,the film thickness of the gate insulating film in terms of the siliconoxide film thickness was found to be 1.6 nm, and the value of theleakage current therethrough, lowered by approximately two orders ofmagnitude, compared with the silicon oxide film with the correspondingfilm thickness.

The present invention provides a semiconductor device havingsimultaneously a plurality of effects such as the improvement on thermalstability of the high-dielectric-constant film, the prevention of thedopant penetration from the gate electrode as well as the prevention ofthe deterioration of electric characteristics of the interface betweenthe gate insulating film and the silicon substrate, by employing a gateinsulating film structure comprising a metal oxide thin film or silicatethin film to which nitrogen addition is applied, the nitrogendistribution therein being kept away from the silicon substrateinterface. Further, the present invention provides a manufacturingmethod capable to fabricate a semiconductor device with a gateinsulating film structure comprising such a high-dielectric-constantthin film as described above.

What is claimed is:
 1. A semiconductor device, comprising: a gateinsulating film and a gate electrode stacked in this order; wherein saidgate insulating film and said gate electrode are in contact with eachother; and wherein said gate insulating film comprises a silicon oxidefilm formed on a silicon substrate so as to be in contact therewith, anda nitrogen containing high-dielectric-constant insulating film formed onsaid silicon oxide film so as to be in contact therewith; and whereinsaid nitrogen containing high-dielectric-constant insulating film whichhas a structure in which nitrogen is introduced into metal oxide ormetal silicate; and wherein a nitrogen concentration in said nitrogencontaining high-dielectric-constant insulating film has a distributionin a direction of a film thickness; and a position at which the nitrogenconcentration in said nitrogen containing high-dielectric-constantinsulating film reaches a maximum in the direction of the film thicknessis present in a region at a distance from the silicon substrate suchthat a maximum impurity concentration of the nitrogen concentration isgreater than a nitrogen concentration at an interface between thesilicon oxide film and the nitrogen containing high-dielectric-constantinsulating film.
 2. The semiconductor device according to claim 1,wherein said position at which the nitrogen concentration in saidnitrogen containing high-dielectric-constant insulating film reaches themaximum in the direction of the film thickness is present in the regionat the distance of not less than 0.5 nm from the silicon substrate. 3.The semiconductor device according to claim 1, wherein said position atwhich the nitrogen concentration in said nitrogen containinghigh-dielectric-constant insulating film reaches the maximum in thedirection of the film thickness is localized on a side of the gateelectrode in said nitrogen containing high-dielectric-constantinsulating film.
 4. The semiconductor device according to claim 1,wherein the position at which the nitrogen concentration in saidnitrogen containing high-dielectric-constant insulating film reaches themaximum in the direction of the film thickness is localized in a centralsection of said nitrogen containing high-dielectric-constant insulatingfilm.
 5. The semiconductor device according to claim 1, wherein thenitrogen concentration on a silicon substrate side interface of saidgate insulating film is less than 3 atomic %.
 6. The semiconductordevice according to claim 1, wherein the position of the maximumimpurity concentration of the nitrogen concentration is present in theregion at a distance from the silicon oxide film.
 7. The semiconductordevice according to claim 1, wherein said silicon substrate and saidgate insulating film are in contact with each other, and said gateinsulating film and said gate electrode are in contact with each other;and said gate electrode is made of either a polysilicon or a polysilicongermanium conductive film.
 8. The semiconductor device according toclaim 1, wherein said gate insulating film contains at least one typeselected from the group consisting of Zr, Hf, Ta, Al, Ti, Nb, Sc, Y, La,Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
 9. Thesemiconductor device according to claim 1, wherein the film thickness ofsaid nitrogen containing high-dielectric-constant insulating film isgreater than a film thickness of said silicon oxide film.